Machines, such as wheel loaders, off-highway trucks and other heavy construction and mining machines, are used to perform many tasks. To effectively perform these tasks, a machine requires a prime mover such as a diesel engine, a gasoline engine, a natural gas engine, a turbine engine or any other type of prime mover that provides the power required to complete these tasks. Some machines include a drive system with a drive motor for powering one or more propulsion devices to propel the machine. Unfortunately, utilizing a single drive motor to propel such a machine may prove inefficient under some circumstances, as various operating conditions may require widely-varying operating speeds and power outputs of the drive motor.
U.S. Pat. No. 4,896,563 (“the '563 patent”) shows a power transmission system with two hydraulic motors and a method of operation that includes operating different combinations of one or both of the motors. The power transmission system of the '563 patent further includes a hydraulic pump for providing power to the hydraulic motors and a planetary gear unit drivingly connected to the hydraulic motors. A first hydraulic motor is drivingly connected to a planet gear carrier of the planetary gear unit, and a second hydraulic motor is drivingly connected to a ring gear of the planetary gear unit.
The '563 patent discloses locking the planet gear carrier to the ring gear, while driving the planet gear carrier with the first hydraulic motor and driving the ring gear with the second hydraulic motor, to drive the sun gear at a first speed. The '563 patent further discloses unlocking the planet gear carrier from the ring gear, deactivating the first hydraulic motor, holding the planet gear carrier stationary, and driving the ring gear with the second hydraulic motor, to drive the sun gear at a second speed, higher than the first. The only use that the '563 patent discloses for the hydraulic pump is supplying the hydraulic motors.
Although the power transmission system of the '563 patent includes multiple hydraulic motors, certain disadvantages persist. For example, by utilizing the hydraulic pump only to supply the hydraulic motors of the power-transmission system, the design fails to capitalize on the hydraulic pump as a potential source of power for other components. Additionally, utilizing only the second hydraulic motor to provide power for high-speed propulsion fails to exploit the power capacity of the first hydraulic motor when power needs may be highest.
The drive system of the present disclosure solves one or more of the problems set forth above.